Metal films formed on a substrate are used in various electric appliances by being pattern-formed.
For conventional methods for forming a metal pattern, mainly a “subtractive method,” a “semi-additive method” and a “full-additive method” are known.
A subtractive method is a method of: providing a photosensitive layer, which is photosensitive to irradiation with actinic radiation, on a metal layer formed on a substrate; carrying out image-wise light-exposure and developing to form a resist image; then etching the metal layer to form a metal pattern; and finally separating the resist therefrom.
In substrates used with this technique, in order to provide adhesiveness between the substrate and the metal layer, roughening treatment is carried out to the substrate interface, and adhesiveness is generated due to an anchoring effect. As a result, the substrate interface portion of the completed metal film is irregular, and so the high frequency characteristics thereof deteriorate when the metal film is used for electrical wiring lines. Furthermore, when forming such a metal substrate, a complicated process of treating the substrate with a strong acid, such as chromic acid, is required in order to carry out roughening treatment of the substrate.
In order to address these issues, a method is proposed for minimizing the irregularities (roughness) of the substrate and for simplifying the treatment process of the substrate. This method involves performing surface modification by grafting a radical polymerizable compound to the substrate surface (see, for example, Patent Document 1, and Non-patent Document 1). However, expensive equipment (such as a γ-ray generator or an electron beam generator) is required for this method. Moreover, since the substrate used by this method is not one to which polymerization initiation groups used as the starting point of graft polymerization are introduced, the graft polymer may not be generated at a sufficient level in practice. Furthermore, even if the metal substrate produced by this technique is patterned using a subtractive process, there are inherent problems with the subtractive method.
That is, in order to form a metal pattern with extremely thin line widths using a subtractive method, an over etching method is effective in which the line width after etching becomes narrower than the line width of the resist pattern itself. However, when attempting to form a fine metal pattern directly by such an over etching method, line smudging, thin spots/cracks, discontinuities and the like readily occur, therefore it is difficult to form metal patterns of 30 μm or less from the viewpoint of forming favorable fine metal patterns. Moreover, wasteful etching processes are required to remove metal thin film from areas other than the pattern portions, and environmental and cost issues arise, such as the expense incurred for treatment of the metal waste fluid produced by such etching processes.
In order to address the above issues, a metal pattern forming technique called a semi-additive method is proposed. With a semi-additive method, a base substrate layer of Cr or the like is thinly formed by metal plating or the like on a substrate, and a resist pattern is formed on the substrate metal layer. Then, after forming a metal layer of Cu or the like by metal plating on the base substrate metal layer in regions other than those of the resist pattern, a wiring pattern is formed by removing the resist pattern. Thereafter, the base substrate metal layer is etched using the wiring pattern as a mask, and a metal pattern is formed in regions other than those of the resist pattern. Since this is an etching-less technique, a fine wiring pattern of 30 μm or less is readily formed, and this technique is effective from the environmental and cost perspectives since metal is only deposited by metal plating in the required portions. However, in order to provide adhesiveness between the substrate and the metal pattern with this technique, roughening treatment of the substrate surface needs to be performed, and as a result the substrate interface portion of the completed metal pattern is irregular, and the high frequency characteristics deteriorate when applied to electrical wiring.
Moreover, a fully-additive process is proposed as a metal pattern forming technique. In a fully-additive process, a resist pattern is formed on a substrate, metal is deposited on regions other than those of the resist pattern by metal plating, and the resist pattern is then removed. Since this technique is also an etching-less technique, a fine wiring pattern of 30 μm or less is readily formed, but there are the same issues as with semi-additive processes.
Accordingly, a new metal pattern forming technique is desired which is capable of forming a fine wiring pattern, has few irregularities of the substrate interface, and produces little etching waste liquid.
Moreover, a fully-additive process is proposed as a metal pattern forming technique. In a fully-additive process, a resist pattern is formed on a substrate, metal is deposited on regions other than those of the resist pattern by metal plating, and the resist pattern is then removed. Since this technique is also an etching-less technique, a fine wiring pattern of 30 μm or less is readily formed, but there are the same issues as with semi-additive processes. Accordingly, a new metal pattern forming technique is desired which is capable of forming a fine wiring pattern, has few irregularities of the substrate interface, and produces little etching waste liquid.
Moreover, increasing the smoothness of an electric conductor surface contributes greatly to increasing density. Surface roughening is performed in conventional build-up printed circuit boards, in order to secure peel strength, but the reality is that such irregularities, of the order of several microns, have become a hindrance to further micronization of wiring lines. In particular, there is a problem of impairing suitability for high frequency transmission in semiconductor devices, with a wiring board using a substrate to which surface roughening has been carried out.
Therefore, a method is desired for forming a fine and dense metal pattern with high adhesiveness on a smooth insulating substrate, for the formation of printed wiring boards applicable to semiconductor devices.
Further, for fine wirings in printed wiring boards and the like, a high insulating property between wirings (electroconductive layers) is also desired.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 58-196238    Non-patent Document 1: “Advanced Materials,” vol. 20, p. 1481-1494, 2000    Non-patent Document 2: “Leading-edge Trend of Micro Junction/wiring Technology” p. 314, published by TORAY RESEARCH CENTER, Inc., November 2003